1. Field of the Invention
The field of the invention is optical detectors for detecting changes in optical density of, i.e., light transmitted through, a liquid flowing through a tubing. More specifically, the present invention relates to an optical detector which is particularly useful in sensing red blood cells in plasma flowing through a tubing in an apparatus for separating whole blood into the components thereof.
2. Description of the Prior Art
Heretofore various optical detectors have been utilized for sensing changes in optical density of a liquid by sensing changes in the light transmitted through the liquid. Such optical detectors have included a light source and a light sensor. An example of one such optical sensor is disclosed in U.S. Pat. No. 3,900,396.
Oftentimes the liquid which is being monitored by the optical detector is passed through a chamber in the optical detector. This requires fluid seals between the tubing and the chamber in the detector.
In an apparatus for processing blood where it is desirable to maintain the blood in a sterile environment and make non-invasive optical measurements of the liquid, such as blood, it is desirable to provide an optical detector which can make optical measurements of light passed through the liquid in a flexible light transmitting tubing which has a generally circular cross section. However, the curved wall portions of the tubing refract and deflect light. Accordingly, it is important to provide means for establishing flat portions of the tubing in the area where light is directed through the tubing so that the light is not refracted or deflected by curved wall portions of the tubing.
Also, it is desirable to provide a simple, inexpensive detector which is highly reliable and highly sensitive so that accurate sensings of red blood cells mixed with plasma can be made by the detector. In this respect, it has been found to be important to provide an optical detector wherein the light source generates a minimum of heat and where the optical detector has means for dissipating any heat so generated so that such heat does not adversely affect the operation of a photosensor utilized in sensing light transmitted through the tubing.
Additionally, it is desirable to monitor the absorbance of blue green light at 550 nanometers wavelength by oxygenated hemoglobin to determine the presence of red blood cells in the plasma since the absorbance of light at that wavelength by other substances carried in the blood is minimal.
As will be described in greater detail hereinafter, the optical detector of the present invention provides a simple, inexpensive, reliable, efficient and highly sensitive optical detector which has a low power light source to minimize the generation of heat by the light source, which has a highly sensitive photosensor and which is constructed in a manner to dissipate heat so generated to prevent such heat from adversely affecting the operation of the photosensor utilized with the optical detector.